When Hydro-Québec’s power grid collapsed on March 13, 1989, a blackout plunged the entire province of Quebec (more than 6 million people) into darkness for several hours. The Event was caused by a violent storm, but the storm was not of Earth’s creation. Instead, the source was the Sun. Our closest star unleashed a swarm of high-energy particles and radiation that wreaked havoc on our technological infrastructure.
But scientists now know that the event was no fluke. Also, it wasn’t particularly powerful. A careful analysis of the evidence gathered from tree rings suggests that similar but much larger barrages repeatedly hit Earth in the relatively recent past. Researchers have long assumed that extreme activity in our star is responsible for these larger events, but new research incorporating insights from tree physiology and the Earth’s carbon cycle suggests: It challenges the idea that solar storms are the cause.
This shift in thinking began about a decade ago when cosmic-ray physicist Fusa Miyake began analyzing long-lived Japanese cedar trees harvested on the island of Yakushima, Japan. Miyake, then a graduate student at Nagoya University in Japan, meticulously extracted carbon-rich cellulose from tree rings. Each ring typically spanned less than a millimeter and he recorded a year’s worth of growth. Her goal was to measure the amount of carbon-14. It is a radioactive isotope of carbon commonly used for dating archaeological artifacts.
Carbon-14, also known as radiocarbon, is produced when high-energy radiation and particles emitted by the sun, other stars, and various cosmic cataclysms interact with atoms, especially nitrogen, in the Earth’s upper atmosphere. , which is naturally generated on Earth. Radiocarbon is also a byproduct of human activity. Atmospheric concentrations of radiocarbon doubled during his mid-20th-century heyday during the Cold War. That’s when America and other nations detonated hundreds of nuclear bombs in the atmosphere.
Radiocarbon is only about one trillionth of the carbon that circulates in Earth’s air, water, and rocks. However, detectable trace amounts of the material accumulate inside trees and other photosynthetic plants, and are still more than enough to be pumped out of the air as carbon dioxide laden with radioisotopes. This makes tree rings a year-by-year record of local environmental conditions and prevailing atmospheric chemistry, allowing scientists to go back thousands of years using well-preserved ancient wood. .
Since the 1950s, researchers have known that the concentration of radiocarbon in tree rings changes over time. But until recently, radiocarbon analysis required relatively large amounts of cellulose, so most measurements were based on five or ten years of his tree rings. Taking cues from previous studies suggesting a significant increase in atmospheric carbon-14 at some point in the late 8th century, Miyake began his survey of individual tree rings from 750 to 820 CE. , she hoped to clarify when and why such events occurred.
Physicist Jesper Olsen of Aarhus University in Denmark says he was not involved in the study. “Nobody thought it was worth it,” he says.
However, Miyake’s efforts paid off, and the data revealed an unusually large increase in carbon-14 concentrations, precisely in 775 AD. Nature Since then, researchers have found additional “Miyake events” in other tree-ring records. Six of his events, the oldest dating to 7176 BC, are particularly well studied, and Miyake events have been used to constrain the timing of various historical events, such as the arrival of the Vikings in the Americas. rice field. However, the origin of the Miyake event remains a mystery. Besides the general consensus that they are caused by some astrophysical process, they have variously been attributed to solar activity, emissions from nearby supernovae or neutron stars, or even Earth’s close encounters with comets. increase.
University of Arizona geoscientist Tim Joule, who was not involved in the study, said giant solar flares are usually cited to explain the Miyake event. Such eruptions of electromagnetic radiation occur regularly on the Sun and are often associated with bursts of high-energy particles. However, this link between solar activity and the Earth’s fluctuating radiocarbon record is blurred by the fact that the Sun also plays a defensive role. The Sun’s magnetic field helps protect the Earth from incoming high-energy particles from outside the solar system and is potentially reduced. Amount of radiocarbon produced from cosmic sources. The shielding is particularly pronounced during the peak of the solar cycle, the 11-year cycle, when the Sun’s magnetic field is strongest.
Benjamin Pope, an astronomer at the University of Queensland in Australia, says one fact is known for sure about Miyake’s event. “They are detections of huge bursts of radiation reaching Earth,” he says. And researchers now know that these explosions outstripped the barrage released in 1989 that crippled Hydro’s Quebec power grid. Pope and his colleagues recently analyzed radiocarbon records from more than 60 of his trees across four continents to explore the nature and origin of these mysterious and alarming signals.The team’s surprising results disrupted Miyake’s already fuzzy understanding of the events, leading to Proceedings of the Royal Society A.
Plotting a series of radiocarbon measurements as a function of time, the Miyake event looks like a cliff that is nearly vertical on one side but slopes more gently on the other. Most miyake events grow very rapidly (often within one tree ring) and then fade away over 10 to 20 years. But that blame is not due to radioactive decay of isotopes, but rather occurs over millennia rather than decades. “It cycles through the carbon cycle,” he adds. After a burst of radiocarbon in the atmosphere, it is eventually buried in seafloor sediments.
Pope and his colleagues realized that to better understand the timing and duration of the Miyake event, a better account of the radiocarbon movement through the global carbon cycle was needed. Researchers have turned to the so-called carbon box model, which consists of a system of differential equations that determine how carbon diffuses through the Earth’s atmosphere, biosphere, oceans, and other reservoirs. I turned it. All of these models attempt to answer a fundamental question, says Pope. “If you put a little radiocarbon into the atmosphere, where will it go?”
Pope and his team started by generating a series of simulated Miyake events. Each event has a slightly different start date, duration, and intensity. We then input that simulated data into several different carbon box models and compare the output with actual radiocarbon measurements obtained from tree rings to arrive at the optimal set of parameters for each Miyake event. converged.
Based on this analysis, most Miyake events appeared to coincide with brief, near-instantaneous ‘spikes’ of radiocarbon production. However, the two events appeared to linger in time. In particular, the one that occurred in 663 BC lasted about three years, researchers concluded. This is perplexing, says Pope, because solar flares, coronal mass ejections, and other eruptions from the Sun typically last only days or weeks. Such relatively short bursts of high-energy particles, he says, are likely to be trapped in one tree ring, which he assembles over the course of a year. Finding evidence for multi-year signals is therefore rather confusing. “God knows what’s going on,” jokes Pope.
But perhaps there’s an explanation that doesn’t involve giving up rapid explosions from the sun, says Tamisa Skoff, a solar physicist at Millersville University. Her answer, she says, may lie in Earth’s complex magnetic field. High-energy particles can be trapped thousands of kilometers above most of the atmosphere. This is so high that it would take years for it to drip down and form radioactive carbon. That may explain why some of Miyake’s events seem so long, Skov says. Perhaps, “some of these longer-duration events could be sources of shorter duration,” she says.
Another explanation for long-lasting miyake events may simply lie in tree physiology, Jules says. When trees begin to grow in the spring, they may rely on nutrients already stored in their cells, he says. This can make seemingly short-lived events, such as pulses of radiocarbon, obscure over time when looking at tree rings. “We have a mix of new and old signals,” Jules says.
Of course, it’s always possible that the multi-year Miyake event could actually be extended, Pope and his colleagues admit. In 2020, another research team, including Miyakebo, proposed that a series of recurring solar flares over several years may be the cause.
Pope and his team were also interested in the exact timing of Miyake events related to the solar cycle. Researchers have shown that solar flares tend to be about four times more likely to occur during solar maxima than during solar minima, suggesting that Miyake events could be clustered near the peak of the solar cycle. One thing makes sense, says Pope. “What I wanted was to say that all this happened during the solar maximum,” he adds. But the team instead found that none of the events were synchronized with the peak of the solar cycle.
But other researchers are still betting that the Miyake events are related to the Sun. It’s not surprising to me that there isn’t one.” After all, during times other than the solar maximum, the Sun can fully fire high-energy particles toward the Earth. It’s a big driving force and we know it tends to show up past the peak of the solar cycle,” says Knipp.
Another idea, Pope and his colleagues hypothesize, is that the Miyake event is associated with a weaker-than-average solar cycle. Scientists have found a decade-long rise in radiocarbon in tree rings dating back to around 5480 BC. It is usually thought that the signal may have been caused by periods of very weak solar activity. Because the Sun’s magnetic field is weaker than average, more energetic particles from interstellar space could have reached Earth during this time.
Tree rings aren’t the only place to look for answers about what happened in Miyake. Some researchers have turned to ice core records to look for beryllium-10 and chlorine-36. These two isotopes, like radiocarbon, are produced in the atmosphere by high-energy phenomena. Australian Nuclear Science and Technology Agency physicist Andrew Smith studies such isotopes in Antarctic ice cores. Drilling from deep within glaciers and ice sheets allows researchers to take photographs of the past year at depths of tens of centimeters from these ice cores, giving researchers more insight into the timing of ancient events. Documentation is available. This allows measurements on a monthly time scale compared to the annual time resolution of tree rings. Smith and his colleagues are currently analyzing data from ice cores with the Miyake event in mind.
The events of Miyake and their origins are still shrouded in mystery and may remain a mystery until they are finally recorded by scientific instruments. But perhaps that’s not the future we want, says Pope. Their sensitive electronics will be fried in nature, Pope said, which could have ripple effects in the areas of navigation and communications. Miyake If or when the next event occurs “Good luck to telecommunications,” he says of what happens.
